Systems employed for particulate sample analysis, such as, but not limited to, those employed in medical and industrial applications to analyze particles in raw materials used to develop final products, customarily include, or are coupled with, some form of sample delivery and mixing apparatus, that `prepares` a respective sample, namely, places it in the physical condition necessary for acceptance and processing through the analyzer. Typically, preparation of a particulate sample involves suspending and separating the particles in a prescribed fluid carrier (such as an aqueous solution), which is then injected into a fluid transport channel for delivery to a particle measurement (e.g., optical illumination-based) subsystem.
For this purpose, as diagrammatically illustrated in FIG. 1, the front end of a sample analyzer 13, having an associated computer workstation 11, includes an input reservoir 12 to which a respective sample 15 is dispensed (for example by way of a sample-retaining test cup, tube or the like 16 to the reservoir by way of a conveyor 17). In order to place the sample particles in a solution for analysis, the reservoir is supplied from a carrier fluid source 21 with a carrier fluid into which the sample is to be mixed, and from a surfactant source 23 with a surfactant that serves to disperse the particles of the sample 15 within the carrier.
A sonic probe (or sonicator) 31 is inserted into the reservoir 12 and which is then stimulated by an ultrasonic drive signal from an energization source 33, so as to cause a sonically induced agitation of the combination of carrier fluid, sample and surfactant. This sonic mixing operation is intended to thoroughly separate and suspend the sample particles in the carrier fluid, so that the mixed contents of the reservoir are in the appropriate physical state required by the sample analyzer 13. Once the analysis has been completed, the reservoir and fluid flow path through the analyzer are subjected to a purging rinse, in preparation for the next sample.
Unfortunately, there are a number of problems associated with such a conventional sample-preparation configuration. One of the most significant is the fact that the sonicator is actually immersed into the fluid contents of the reservoir. Because the volume of the reservoir is relatively large, the sonic energy emitted by the probe is reduced as it diffuses into the contents of the reservoir. This means that a relatively large amount of probe drive energy is necessary to obtain thorough mixing of the sample in the carrier, resulting in poor efficiency of the sonicator operation.
In addition, because the probe is immersed into the mixture, it not only may displace some of the sample, but itself becomes coated with sample and surfactant, and therefore requires cleaning after each use. Moreover, depending upon the application, the mixture into which the probe is inserted may be corrosive to the probe, which shortens the life of the probe.